Global temperature rise of 8 degrees possible by 2100

Nov. 9, 2012
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The sign at the Clovis Memorial District building reads 107 degrees on Aug. 10 in Clovis, Calif. Temperatures soared into triple digits across the western United States. / Craig Kohlruss, The Fresno (Calif.) Bee, via AP

by Doyle Rice, USA TODAY

by Doyle Rice, USA TODAY

As the USA swelters through its hottest year on record - and the Earth sees yet another top-10 year for heat - a study published today in the journal Science says we'd better get used to it.

The study finds that future temperature rises due to global warming will probably be on the high end of projections, as much as a potentially catastrophic 8 degrees warmer than now by the end of the century.

Most predictions of upcoming temperature rises are roughly 3.6 degrees to 8.1 degrees.

Study co-authors John Fasullo and Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo., reached their conclusions by looking at how well 16 top climate computer models reproduced actual relative humidity in the tropics and subtropics, as measured by satellites.

Higher levels of humidity tend to produce clouds, which remain one of the most vexing aspects of predicting future climate. Though additional clouds can cause temperatures to cool as less heat reaches the ground, they can also act to increase the heat that's trapped below them. In their study, the scientists used humidity as a substitute for clouds, since models cannot accurately forecast cloud cover.

"There is a striking relationship between how well climate models simulate relative humidity in key areas and how much warming they show in response to increasing carbon dioxide," Fasullo says. "Given how fundamental these processes are to clouds and the overall global climate, our findings indicate that warming is likely to be on the high side of current projections."

Warmer temperature would bring greater impacts on society, they say, in terms of a rise in sea level, heat waves, droughts and other threats.

Since about 1900, the average temperature of the Earth's surface has risen by roughly 1.4 degrees, and close to two-thirds of the increase has occurred since 1980, according to a National Academy of Sciences report.